Etching apparatus for making a cellulosic printing plate



Se t. 6, 1966 H. c. STAEHLE ETAL 3,

ETCHING APPARATUS FOR MAKING A CELLULOSIC PRINTING PLATE Filed Aug. 9,1963 5 Sheets-Sheet 1 Fl LTER Fig.1 /63 Henry C. S faehle Cyril A.HorfonLinc0lnA.Gandall Harold J Frelier INVENTORS ATTORNEYS Sept. 6, 1966 H.c. STAEHLE ETAL 3,271,226

ETCHING APPARATUS FOR MAKING A GELLULOSIC PRINTING PLATE Filed Aug. 9,1963 5 Sheets-Sheet 2 FigzZ Henry C. Staehle Cyril A-Hort on LincolnA.G'undall Harold J Fre lier INVENTORY Sept. 6, 1966 H. c. STAEHLE ETAL3,

ETCHING APPARATUS FOR MAKING A CELLULOSIC PRINTING PLATE Filed Aug. 9,1963 I3 Sheets-Sheet 5 Henry C. Siaehle Cyril A.H0rl'0n Linc0lnA.CundallHarold JFrelier INVENIORS JQTTORNEY'S United States Patent 3,271,226ETCHHNG APPARATUS FOR MAKING A CELLU- LOSiC PRHNTENG PLATE Henry C.Staehle, Lincoln A. Cundall, Cyril A. Horton, and Harold .l'. Frelier,Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., acorporation of New Jersey Filed Aug. 9, 1963, Ser. No. 300,977 12Claims. (Cl. 156345) This invention relates to halftone printing andparticularly to an arrangement for solvent etching a relief halftone ina cellulosic sheet protected by a suitable resist stencil such as aphotographically produced washoif gelatin image.

Relief plates of cellulose nitrate or of cellulose esters such ascellulose acetate are known, and solvent etching of the latter type isdescribed in US. Patent 2,891,849, Whitbourne. The present invention isdirectly useful with the process described in the Whitbourne patent.

While the removal of material between the dots of a relief printingplate is normally referred to as etching, the actual operation is asoftening of the cellulosic sheet by the solvent accompanied by abrushing to remove the softened areas. With hundred-line halftones orfiner, the hairs of the brush must be quite small to operate between thedots, even in the highlight regions where the dots are small, andparticularly in the shadow regions where the dots merge and the materialto be removed leaves only a small hole. In the Whitbourne patentmentioned above, a nylon velvet pad is suggested as the brush, and sucha pad is ideally useful with the present invention.

The primary object of the present invention is to provide an improvedand reliable etching arrangement producing a printing plate withexcellent dot quality. The etching including brushing according to thepresent invention is so efficient that good gradation is produced in theshadows, and the light tones or highlights are reliably produced with aminimum of loss of fine highlight dots.

It is a particular object of the invention to permit several successiveetching steps or bites of the plate without adversely affecting thehighlight dots.

A further object of the invention is to provide an automatic orsemi-automatic apparatus into which a plate ready for one or moreetching steps can be fed and which will provide just the right degree ofetching. Specifically, the invention employs a rotatable drum supportinga plate to be etched and carrying the plate past a plush belt whichapplied etchant and simultaneously wipes softened material from theplate.

One form of such plate consists of a relatively thick acetate sheetcoated with a light-sensitive or sensitized gelatin layer.Alternatively, it is now common to use a laminate in which the celluloseacetate sheet or other plastic sheet is supported by a thin metal plate,but as far as the present invention is concerned, as long as thecellulose acetate sheet or layer is fairly rigid, it does not matterwhich form is used. On the other hand, a preferred embodiment grips thesupporting plate magnetically, and hence the embodiment requires theferrous metal base. Several specific examples of printing platesetchable by the present invention are set forth in the copendingapplication for Letters Patent Serial No. 269,345, filed April 1, 1963,in the names of C. D. Baxter and H. C. Staehle. The invention will bedescribed with respect to a cellulose acetate sheet, but it is equallyapplicable to any material which employs solvent etching accompanied byvelvet brushing. Cellulosic layer as used hereinafter is intended toinclude all such suitable plastic or lacquer materials. A cellulosicplate consists essentially of such a layer self-supported or laminatedto another support such as a metal sheet.

The light-sensitive gelatin layer may be of any of the forms used forthe production of stencils. It is not necessary for the residual gelatinimage or stencil to be clear. Accordingly, it is preferable to use oneof the more efficient types of recording system, namely that in which asilver salt is incorporated in the gelatin and in which a developerhardens the gelatin adjacent to the silver at the time the silver saltis reduced to silver. Such a cellulosic plate is exposed, for example,to a halftone negative. The exposed areas are developed with any of thestandard hardening or tanning developers which reduce the silver salt tometallic silver and which harden the adjacent gelatin. The remaininggelatin is washed off, but the silver is not bleached out, although itcould be bleached out. One advantage of leaving the silver in thehardened gelatin is that the image (laterally inverted but positive) isimmediately apparent on the plate and the quality can be easily judged.The unexposed areas of the plate are then removed by washing in warmwater, just warm enough to remove the unhardened gelatin but not warmenough to remove the hardened areas. This is all well known.

Due to such removal of the unh-ardened gelatin (plus any residual silversalt therein), the cellulose acetate surface is now exposed (directly orthrough a thin subbing layer which is also soluble in the solventetchant to be used) in the areas to be etched, but it is still coveredwith the hardened gel-atin and-silver stencil in the areas which are notto be etched. In practice, at least some of the gelatin-silver layerremains on the finished plate and is inked for printing, but even if thegelatin layer is worn away, the top surface of the cellulose acetatedots may be inked and prints pulled therefrom.

The present invention starts with an exposed, developed and washed-offplate consisting essentially of a cellulosic layer with a stencilthereon which is not soluble in the solvents to be used for softeningthe cellulosic layer. For example, the Whitbourne patent and the Baxteret al. application mentioned above describe some suitable solventshereinafter referred to as etchant for cellulose acetate which do notattack the gelatin stencil. For simplicity, the developed andwashed-off, but not etched, plate is hereinafter referred to as acellulosic plate with a developed stencil thereon. The present inventionstarts with such a cellulosic plate and stencil and finishes with acompleted etched plate ready for inking and printing therefrom.

In accordance with the invention, a cellulosic plate with developedstencil thereon is secured to the surface of a drivable drum, whichengages, throughout its lowest segment, a plush belt continuouslymoistened with an etchant. Since the particular etchants used areineffective without scrubbing, the belt is driven at a speed differentfrom and in a plurality of directions relative to that of the plate sothat the pile of the belt continuously rubs against a major surface ofthe plate to apply etchant thereto and to remove softened portions ofthe plate between resistant nodules or dots of the developed and tannedstencil. As the drum continues to rotate, moving the plate past theplush belt, the plate is wiped to remove excess etchant, dried byauxiliary heaters, and allowed to cool prior to a next engagement of theetchant applied by the plush belt.

The subject matter which is regarded .as our inventi-on is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. The invention, however, as to its organization andoperation together with further objects and advantages thereof, willbest be understood by reference to the following description taken inconnection with the accompanying drawings in which:

FIG. 1 is an elevation view partially in section of the etchingarrangement of the present invention;

' FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a detail view of the surface construction of the roller shownin FIGS. 1 and 2; and

FIG. 4 is a magnified perspective view of a small segment of a partiallyetched ha-lftone plate being engaged by the plush bristles.

Referring now to the drawings wherein like numbers refer to similarparts, we have shown in FIGS. 1 and 2 a main drum 10 having an outersurface comprising a layer of magnetic materials 11 and a layer ofinsulation means such as cork 12 covered by a gummed kraft paper tape13. This construction is such that a cellulosic plate 14 having amagnetizable base will adhere thereto. In the overall constructionillustrated, one side of the drum 10 is exposed to facilitate placingthe plate 14 thereon and observation of the plate during etching.

As shown more clearly in FIG. 3, the magnetic material 11 may take theform of wide, A" thick Koroseal flexible strips marketed by B. F.Goodrich as Pole #3. These strips are helica'lly applied with the northpoles adjacent to the north poles as indicated. In one embodiment, thelayer of cork 12 is 4; thick, and with the kraft tape 13, providessutficient insulation to allow the heating and cooling cycle discussedbelow without damage to the composite drum 10.

The drum 10 with the plate 14 supported thereon is driven in a clockwisedirection (FIG. 2) as indicated by an arrow 16 .by a driving means suchas a mot-or 17. Throughout the surface region of the lower segment ofthe plate 14 is positioned a plush belt 18 supported by a pair ofrollers 20 and 21 with the roller 21 being driven by a reversible motor22 so that the surface of the plush belt 18 wipes in both directionsacross the lower surface of the cellulosic plate 14. The rollers 20 and21 and the plush belt 18 lie partially within a pan 24 having therein anetchant 26 such as is used for thinning lacquer and specifically setforth in the abovementioned patent application Serial No. 269,345. Thelevel of the etchant 26 is sufficient to engage the lower surface of theplush belt 18 whereby the plush 18 applies the etchant to the plate 14.The generally horizontal placement of the plush belt 1 8, asdistinguished from a vertical placement, reduces to a minimum thevertical lift of the etchant. Such construction reduces solventevaporation and drying out of the belt, as well as allowing lateralaccess and observation. The etchant is replenished periodically, beingapplied directly to the belt 1 8 from a distributor pipe 27. In order toprevent build-up of slag on the belt 18, we have provided a plurality ofvanes 28 which agitate the pile while it is within the etchant bath 26.

One plush fabric which works satisfactorily in this invention is amohair plush, having a pile. As the etchant softens portions of theplate 1 4 between the resistant developed nodules 30 (FIG. 4), laterbristles 32 of the plush belt 18 wipe away the softened plastic betweenthe nodules 30. However, the hard nodules 30 apparently deflect thebristles as at 32' and prevent them from wiping away plastic materialunder the nodules 30. As a result, when the etching under the complete,the nodules 30 become supported by a conical configuration, of a heightof the order of .01 inch as indicated by the dashed lines 34. Etching aprinting plate as much as .01 inch is usually considered necessary toobtain excellent halftone reproductions when using certain printingtechniques.

As is shown in FIG. 4, the plate 14 includes a base layer 36. This baselayer is preferably of a magnetizable metal such as iron alloys and ofsufficient strength to allow handling, etc. The iron base layer 36enhances 4 securing the plate 1 4 to the magnetic surface of the drum10.

Because of the softening effect of the etchant on the plastic below eachnodule, it is not practicable to complete the etching step in one bite,whereby the etchant would soften all of the plastic so that the nodules30 as well as the plastic therearound would be wiped away by thebristles 32. Usually, when providing fine relief printing plates, onlyabout .001 may be removed per bite without damage or loss of some of thefinest nodules 30. The magnified view of FIG. 4 represents theappearance of the plate after several bites have been taken, with thenodules 30 being about .001 in diameter and the maximum depth (34) ofetching about .01". When operating at room temperature, the drum 10 isdriven at a speed such as r.p.m., which is substantially greater thanthat necessary to remove the full depth of the etching required forprinting purposes during a single pass over the plush belt 18. Theacceptable duration of application of etchant, and therefore the speedof rotation of the drum 10, is primarily a function of the fineness ofdetail of the developed plate 14. When etching a halftone of lines perinch, 4 rpm. is suitable, while halftones of 40 lines per inch may beetched at rpm.

During the etching process, the surface of the belt 18 travels at about120 feet per minute and is reversed about 30 times per minute. As thesuccessive portions of the plate 14 leave the region of the plush belt18, they are wiped by a plush roller 42 to remove substantially all ofthe etchant remaining. As it is rotated in a clockwise direction by adriving motor 43, the plush roller 42 is wiped clean by a rigid wiper44. During certain types of operations, a wiper 45 may replace the plushroller 42 or be used in conjunction with it. Used etchant removed fromthe plate 14 by the roller 42 and collected on the wiper 44 flows into atrough 46. Such waste is directed by an outlet pipe 47 from the trough46 to a waste material collection receptacle.

As the plate 14 continues to revolve, the etching action may be haltedby application of certain non-solvents such as alcohols applied theretoby a nozzle 49 with excess alcohol falling against a shield 50 anddraining from the shield to another waste receptacle (not shown). Whenusing volatile etchants such as ethyl acetate or n-butyl acetate and aneflicient drying arrangement, as discussed below, application of thealcohol may be omitted.

During further rotation, in order to assure drying of the partiallyetched plate 14, the plate surface is heated by suitable means so that anext bite may be taken by the plush belt 18 without loss of detail. Theparticular drying apparatus shown in FIG. 2 is a combination hot air andradiant heater system. The hot air portion utilizes a plurality ofparallel pipes 54 having inwardly opening apertures 55 which direct air,heated to temperatures of the order of 200 F., against the surfaces ofthe plate 14. The radiant heaters 56 must be operated at temperaturesbelow the ignition temperatures, such as 700 F., of the chemicals beingused. The heating operation must be further controlled to preventblistering of the developed plate 14 by limiting the maximum temperaturethereof. Temperatures above about 200 F. tend to blister the plate, andwe have provided a temperature sensing means such as a thermocouple or athermistor 60 on the cork 12 to sense the temperature of the plate 14and limit the effectiveness of the heating means when temperatures ofabout F. are reached.

Because of the fact that the etchant (and the alcohol when used) tendsto create noxious and inflammable fumes, we have provided exhaust meanssubstantially surrounding the pipes 54 and the heaters 56 in the form ofan exhaust hood 57 with a fan 58 (FIG. 1) for removing the heated aircontaining the volatile solvents. Usually, this contaminated air isremoved both from the region of the etching arrangement and from thebuilding housing the equipment.

As shown more clearly in FIG. I, the inlet to the hot air pipes 54comprises a filter 62, a fan 63, a heater 64 and duct means 65 whichconveys the heated air to both ends of the hood 57 wherein plenumchamber distributors 66 convey air to both of the ends of each of thepipes 54. In order to assure removal of noxious fumes, the capacity ofthe fan 58 is made larger than that of the fan 63.

As a final stage, during each bite, the plate 14 is cooled to near roomtemperature prior to the next bite. Auxiliary cooling means such as coolair impingement is obtained from a distributor pipe 68 to assuresuitable cooling. Depending on the time duration between the heatersystem and the plush belt 18, additional or no cooling means may beemployed.

We have found that during etching simply scrubbing the surface of thedeveloped plate 14 with a continuous straight wiping action preventsobtaining of useful etched plates. Such wiping results in deep ridgeswhich branch and combine in the manner of mountain ranges without regardto the size or location of the developed nodules 30 or other printedmatter. This action invariably results in high ridges in large whitespaces which provides a wrinkled appearance in margins, etc., of printspulled from a finished plate. However, by driving the plush belt 18laterally (generally perpendicular to the motion of the nearest portionof the drum surface) by means of the type illustrated in FIG. 1, whileit travels over the rollers 20 and 21, a sinusoidal scrubbing action isattainable whereby the bristles 32 engage all surfaces of each cone inthe region of the nodules 30 to obtain the conical etching as indicatedin FIG. 4 and substantially smooth etching of undeveloped spaces in theplate 14.

The lateral drive of the plush belt 18 is preferably accomplished by aneccentric drive 70 connected by a lever 72 to a drive arm 73 of asupport 74 for the bearings 75 of the rollers 20 and 21. We have found aspeed of 60 r.p.m. suitable for the eccentric drive 70 when the lengthof its stroke is of the order of 1.00". The motion of the frame 74 isfacilitated by the use of rollers 76 and 77 (FIG. 2). Obviously, withsuch motion of the support 74, the motor 22 will be most effective if itis mounted on the support 74 or provided wit-h a universal drive linkage78, as shown in FIG. 1.

An additional control feature enhances the attaining of quality plates,and that is regulation of the pressure between the plush belt 18 and thedrum 10. Both the total pressure and the distributed pressure areimportant. .The total pressure is regulated by upward force developed bythe support plates 80 of the rollers 76. We prefer to use pneumaticmeans such as air cylinders 82 to regulate this force. The distributedpressure is a function of the sag of the plush belt 18 between therollers 20 and 21. This sag is most easily regulated by a turnbuckledrive arrangement 84 shown in phantom in FIG. 2. The location of therollers 20 and 21 is critical in the sense that the rollers should notdirectly drive the plush belt 18 against the plate 14 with any greaterforce than that applied by the belt in regions between the rollers. Withthe belt 18 being of considerable strength, this spacing requires slightadjustment only once every few days and the spacing between the rollers20 and 21 and the plate 14 may be observed during operation to detectexcessive sag.

Another feature which simplifies maintenance is the use of removablebearing blocks in the bearings 75 so that the belt 18 may be removedeasily.

While we have shown and described particular embodiments of the presentinvention, other modifications may occur to those skilled in this art.For instance, it is preferable to arrange the air cylinders 82, or otherlevel control means, so that the pan 24 and belt 18 maybe loweredsufiiciently to allow placing a cover thereover when the machine is notin use. Such a cover reduces solvent loss and concurrent explosionrisks. Similarly, the main drum could be replaced by a combination ofseveral smaller rollers and an endless belt drivable thereby. Such aconstruction would somewhat simplify the drive of the plush belt 18 inthat it could be conveyed over a flat bed instead of having distributedsag as discussed above. However, the overall construction andmaintenance costs of such a system tend to be more expensive and are notpreferred. We intend, therefore, to have the appended claims cover allmodifications which fall Within the true spirit and scope of ourinvention.

We claim:

1. An etching apparatus for etching in a plurality of bites a reliefprinting plate including a cellulosic layer having a resist stencillayer thereon, comprising;

a rotatable drum for supporting the plate with the stencil layer facingoutward;

a plush belt drivable to scrub the surface of the plate during rotationof said drum and having bristles fine enough to engage each of theexposed areas of the cellulosic layer;

means for wetting said belt with etchant during its scrubbing of theplate for softening the exposed cellulosic areas; and

means for driving said belt at surface velocities difierent from that ofthe plate on said drum and in a plurality of directions relative to thesurface of the plate so that the softened portions are scrubbed away bythe bristles on all sides of each stencil nodule of the stencil layer.

2. An etching apparatus for forming a relief printing plate by etchingthe exposed portions of a cellulosic layer having a stencil on itssurface, comprising:

a rotatable drum for supporting the plate on the drum periphery with thestencil layer facing outward;

a plush belt mounted to engage the periphery of a segment of said drumand drivable at a speed difierent from that of the drum periphery toapply etchant and to scrub the surface of the cellulosic layer, saidbelt having plush bristles fine enough to engage each of the exposedportions of the cellulosic layer;

means for wetting said plush belt with an etchant which softens only theexposed cellulosic layer;

means for driving said plush belt at surface velocities different fromthat of the plate on said drum and in a plurality of directions relativethereto so that softened portions of the cellulosic layer are scrubbedaway by the bristles;

cleaning means for removing etchant after said drum has conveyed theplate beyond the region of engagement by said belt;

heater means for drying the cleaned plate; and

means rotating said drum to repeatedly move the plate within the regionof engagement of said belt, said cleaning means and said heater means insequence to thus obtain a plurality of etching bites without loss ofstencill regions as small as .001" in diameter.

3. An etching apparatus according to claim 2 wherein the plate includesa base layer of magnetizable material and said drum comprises:

a magnetic layer for supporting the plate.

4. An etching apparatus according to claim 3 wherein said drum includesa layer of thermal insulation covering said magnetic layer.

5. An etching apparatus according to claim 2 wherein said cleaning meansincludes a plush roller which scrubs the surface of the cellulosic layerand a rigid wiper bar which removes waste material from said plushroller.

6. An etching apparatus according to claim 2 wherein said Wetting meansincludes a pan containing etchant, the pan being positioned to haveetchant therein engage a portion of said plush belt during the scrubbingof the plate by another portion of said belt.

7. An etching apparatus according to claim 2 wherein said heater meansincludes hot air flow control means for removing heated air containingetchant vapors.

8. An etching apparatus according to claim 2 wherein said heater meansincludes hot air impingement means for directing heated air against theexposed surface of the plate. 9. An etching apparatus according to claim2 wherein said belt is supported on a pair of spaced apart rollers whichare in turn supported on bearing means which cooperate therewith toregulate the overall pressure and the distributed pressure between saidbelt and said drum.

10. An etching apparatus according to claim 9 wherein means are providedto drive said bearing means laterally in a motion generallyperpendicular to the motion of said drum surface whereby the scrubbingaction is a reversing sinusoidal action.

11. An etc-hing apparatus according to claim 6 including means forwetting said plush belt with fresh etchant during the scrubbing of theplate and wherein said pan will store sufficient etchant to continuallywet said belt.

12. An etching apparatus accordng to claim 11 including a vane withinsaid pan to engage said belt and flex the bristles thereof to removecellulosic matter scrubbed from said plate.

References Cited by the Examiner UNITED STATES PATENTS 2,604,024 7/1952Luboshez. 2,891,849 6/1959 Whitbourne l5613 ALEXANDER WY'MAN, PrimaryExaminer. JACOB STEINBERG, Examiner.

1. AN ETCHING APPARATUS FOR ETCHING IN A PLURALITY OF BITES A RELIEFPRINTING PLATE INCLUDING A CELLULOSIC LAYER HAVING A RESIST STENCILLAYER THEREON, COMPRISING; A ROTATABLE DRUM FOR SUPPORTING THE PLATEWITH THE STENCIL LAYER FACING OUTWARD; A PLUSH BELT DRIVABLE TO SCRUBTHE SURFACE OF THE PLATE DURING ROTATION OF SAID DRUM AND HAVINGBRISTLES FINE ENOUGH TO ENGAGE EACH OF THE EXPOSED AREAS OF THECELLULOSIC LAYER; MEANS FOR WETTING SAID BELT WITH ETCHANT DURING ITSSCRUBBING OF THE PLATE FOR SOFTENING THE EXPOSED CELLULOSIC AREAS; ANDMEANS FOR DRIVING SAID BELT AT SURFACES VELOCITIES DIFFERENT FROM THATOF THE PLATE ON SAID DRUM AND IN A PLURALITY OF DIRECTIONS RELATIVE TOTHE SURFACE OF THE PLATE SO THAT THE SOFTENED PORTIONS ARE SCRUBBED AWAYBY THE BRISTLES ON ALL SIDES OF EACH STENCIL NODULE OF THE STENCILLAYER.